A conventional deceleration device may include a cam mechanism that moves the position where a first gear and a second gear are engaged in accordance with the received drive torque. The number of teeth of the first gear differs from the number of teeth of the second gear. One of an inner teeth gear and an outer teeth gear is the first gear, and the other one of the inner and outer teeth gears is the second gear. The cam mechanism is coaxial with the first gear and rotationally supported by the first gear. The cam mechanism is capable of engaging the first gear with the second gear in an eccentric state and moving the engaged position of the first gear and the second gear in accordance with the received drive torque.
In such a deceleration device, when the engaged position of the first gear and the second gear moves, the first and second gears rotate relative to each other to decelerate rotation drive received by the cam mechanism at a high deceleration ratio. For example, Patent Document 1 discloses a seat drive device in which such a deceleration device is located between a seat cushion and a seat back so that the seat drive device functions as a reclining device capable of adjusting an inclination angle of the seat back.
More specifically, in the seat drive device, the deceleration device that forms the reclining device includes a first member including the inner teeth gear, which is the first gear, and a second member including the outer teeth gear, which is the second gear. The first member is fixed to the seat back, and the second member is fixed to the seat cushion. Further, such a reclining device is often arranged at each lateral side of the seat back. In the two reclining devices, a coupling shaft extending in the lateral direction of the seat couples the cam mechanisms that are coaxial with the inner teeth gear (first gear).
Further, the conventional seat drive device includes an actuator device that decelerates the rotation produced by a motor serving as a drive source and outputs the decelerated rotation. For example, the actuator device is fixed to one side of the seat cushion, and a deceleration gear of the actuator device is arranged coaxially with the outer teeth gear (second gear) of the deceleration device that forms the reclining device. The deceleration gear includes a coupling hole for the coupling shaft arranged at an eccentric position that is separated from the rotation center.
More specifically, in the deceleration device of each of the reclining devices, when one of the first gear and the second gear is set as a reference, the other one virtually swings and rotates over a predetermined eccentricity amount that is set between the two gears.
Thus, in the conventional seat drive device, the coupling hole is formed in advance at a predetermined eccentric position corresponding to the eccentricity amount, and the coupling shaft is coupled to the deceleration gear serving as a rotor that receives drive torque. As a result, the coupling shaft revolves around the rotation shaft of the rotor. This allows the drive torque of the actuator device, which is arranged on the non-rotatable seat cushion, to be transmitted to the cam mechanism of each reclining device that swings and rotates with the seat back.